Differential adjustment



3 Sheets-Sheet l Jan. 26, 1943. s, cRguM DIFFERENTIAL ADJUSTMENT Filedoct. 15. 1959 jfSnmtar S 'zp h. en. Crum Gtorngg IIIIL 33 82 lemeeee'l"VHH'H Jan. 26,1943. s. CRUM DIFFERENTIAL ADJUSTMENT 5 Sheets-Sheet 2 mJ1 mm ,/fn Imm mA m. ..n wm w l L.. o sph@ Jan' 26,- 1943- s. CRUM369,169

v DIFFERENTIAL ADJUSTMENT l mnd'oq. 13. 1959' s sheets-sheet s mnntorSigel/Lem.v Cum.

Patented Jan. 26, 1943 DIFFERENTIAL ADJUSTMENT Stephen Crum,Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company,Minneapolis, Minn., a corporation of Delaware Application October 13,1939, Serial No. 299,316

Claims.

This invention is directed broadly to a novel type of differentialadjustment and deals more specically with a meansfor adjusting theoperating dilierential of a condition responsive mercury switch.

Differential adjustments are old and well known in the prior art, butthese adjustments are either difficult to make or else are so located asto require expert manipulation in order to avoid injury to the device.For example, where the differential'adjustment is made by varying therelative positions of twor members which are moved by the conditionresponsive element and which form a part of the driving connectionsbetween the element and the switch, the actual adjustment by means of ascrew-driver or wrench is very apt to distort and strain the conditionresponsive element due to the fact that the element is usuallycomparatively delicate and a relatively great force must be appliedtorelease the part to be adjusted and then x it in its new position. Greatcare must be taken under these circumstances because any accidentalmovement of the screw-driver or wrench may so distort the responsiveelement as to give it a permanent set which would destroy* thecalibrationof the switch.

Adjustments of condition responsive switches' are frequently made byunskilled persons who are unfamiliar with the construction oi? thedevices and who would therefore not be likely to exert the care andskill necessary for making these adjustments. It is therefore a. primaryobject of this invention to provide a condition responsive switch havinga means for adjusting the differential of operation which is simple inconstruction, easy to manipulate, and which cannot damage either thedriving connections or the responsive element no matter how carelesslythe adjustment is made.

Another object of the invention is to provide a condition responsiveswitch in which the movable parts of the differential adjustment aremounted directly to a fixed plate Within the instrumentv l cessivestrain on the element on overrun of the Aconditionl value.

A further object of the invention, as exoverrun of the operatingconnections and mercury switch on abnormally great variations in thecondition value thereby eliminating the necessity for a strain releaseconnection to the condition responsive element.

Further objects reside in the combination of elements and the details ofconstruction.

For a clearer understanding of the invention reference is made to thespecification taken in the light of the accompanying drawings in whichFigure l is a side view taken partially in section of one form of myinvention as applied to a thermostatically operated switch having ahorizontal mounting,

Figure 2 is a front elevation of part of the mechanism shown in Figure1,

' Figure 3 is a rear elevation' ofJ the mechanism shown in Figure 2,

Figure 4 is a detail view of the scissors type strain release,

Figure 5 is a rear elevation partly in section of my invention asapplied to a thermostatlcally operated switch having a verticalmounting,

Figure 6 is a front elevation of the modification shown in Figure 5,

Figure 7 is an exploded view of a further modication of my invention asapplied to a horizontal mounting,

Figure 8 is a rear view of a portion of the mechanism shown in Figure 7,and

Figures 9, 10 and 11 are more or less diagrammatic views showing themechanism in various positions of operation.

The invention has been illustrated and Will be described in thefollowing specification as a biengage in holes I4 in the base I I tomaintain the` cover in position on the base.

The base I I is provided with an opening l5, and

a guard I6 is connected to the base Il around the emplified in amodification, is to provide for an hole I5 and projects rearwardly fromthe base.

Rotatably mounted in the hole I5 is asleeve I 'l which is connected atits inner end to an adjustlwhich a washer 24 seats.

an annular depression which is adapted to slide frictionally on abearing washer 2| which lies against the back of the base il about thehole i5. A guide sleeve 22 is provided with a narrow portion which isinserted within the end of the sleeves |1 and a wide portion 23 againstA retaining spring 25 is provided with a hole 26 which receives the endof the member 22 and the ends of the retaining spring 25 are engaged inholes n opposite sides of the base l as illustrated in my copendingapplication Serial No. 299.315 and filed October 13, 1939.

The outer end of the sleeve |1 has an inturned portion 3D and aprojection 3| to which one end of birnetallic helix 33 is connected bymeans of theI screw 32. The other end of the bimetallic heliz; 33 isconnected to an actuating rod 34 by means of the screw 35 and thisactuating rod extends through a hole in the portion 30 of the sleeve l1,through the sleeve |1 and the guide sleeve 22 and within the casing |U.The inner end of the rod 34 carries an actuating member in the form of ascisso-rs type strain release generally indicated at 31.

The scissors type strain release is in the form of a hub 38 having anarrow stem portion 39 to which an L-shaped stop 40 is rigidlyconnected. Rotatably mounted on the stem portion 39 are a pair offingers 4| and 42. t resilient spring is wound several times around thestem 39 and one end of the spring 43 is inserted through a hole in themember 4| and the other end of the spring 43 is inserted through a holein the finger 42, the effect of the spring being to resiliently hold thelingers 4l and 42 in engagement with the L- shaped stop 48.

A plate 45 is rigidly connected to the base by means of the posts 45 and41 which are lxed to the base by means of screws 48. A mercury switchcarrier 49 is pivotally mounted to the plate 45 by means of the shaft58. The carrier 49 supports the mercury switch 5| by means of the clip52 so that as the member 49 is rotated back and forth the mercury switch5| is moved between open and closed positions. The mercury switchcarrier 49 is provided with a rearwardly extending portion 55 andlaterally extending portion 55 and a shaft 51 extending between the mainportion of the carriei` 49 and the laterally extending portion 56pivotally carries a lever 58.

The plate 45 is provided with a circular opening 59 which receives thehub 38 of theV strain release 3l. lThe hole 59 has an extension whichreceives a pin 8D which is carried by a mid portion of the lever 58. Theupper end of the lever 58 carries a pin 6| which extends between the twofingers 4| and 42 of the strain release 31.

The pin B8 is free to move from one side S3 to the other side 54 of theextension of the opening 59. In order to adjust the limit of movement ofthe pin 6D toward the side 64 of the opening 59 a lever 66 is providedwhich is pivoted on a shaft 58 and a spring 61 resists rotation of thelever. This lever is provided with a shoulder 68 against which the pinwill rest under certain conditions of adjustment of the lever. This willbe more fully described later. The lever B8 is provided with a forwardlyprojecting finger 10 byfmeans of which it may be rotated about the shaft58 and this finger cooperates with a scale 1| carried by the plate 45which may indicate the relative adjustment of the lever.

A main adjusting arm 12 seats on a small shoulder on the guiding sleeve22 for rotation about the rod 34 as a center and is adjustably securedto a projection 13 on the adjusting disc I8 by means of a screw 89 whichthreads into a tapped hole 14 in the projection 13 and extends through aclearance slot 15 in the adjusting arm 12. The adjusting arm 12 isgenerally U-shaped and the forward portion is provided with a head 16having a kerf 11 so that it may be rotated by means of a screw-driver.The head 16 projects through a hole 18 in the front of the cover so thatthe adjustment may be made without removing the cover. The cover may beprovided with a window 19 so that a portion 80 of the arm 12 may beseen. This portion 80 may carry a scale to indicate the relativeadjustment of the arm. The arm 12 is provided with a hole 8| toaccommodate the blade of a screw-driver for loosening the screw 69 inorder to relatively adjust the arm 12 and the adjusting disc |9.

In considering the operation of the above device let it be assumed thatthe temperature is at a relatively high value and that the thermostat 33has rotated the lever 58 in a. counter-clockwise direction as viewed inFigure 2 and that the mercury switch 5| is in open position. Further,let it be assumed that the lever 10 is adjusted as seen in Figures 2 and3 to permit a relative movement of the pin 60 between the shoulders 63and 68. On a decrease in temperature the bimetallic thermostat 33 willcool and move the pin 6| on the upper end of the lever 58 toward theright as seen in Figure 2. During this time the lever 58 will rotatefreely about the shaft 51 and the pin 60 which was in engagement withthe shoulder 63 will move toward the shoulder 68. As this operationtakes place the lever 58 is rotating freely and is having no effect uponthe mercury vswitch carrier 49. After the pin 60 has engaged theshoulder B8 on the lever 56 this free rotation wise direction willresult o1' the lever 58 can no longer take place and a further movementof the pin 8| toward the right as seen in Figure 2 will result in arotation of the lower end of the lever toward the left as seen in Figure2, or in other words, the lever will be rotating in a clockwisedirection and the shaft 51 will be swinging about the shaft 50 as acenter. This swinging motion of the lower end of the lever 58 willresult in the rotation of the mercury switch carrier 49 about the shaft50 and will result in tilting the mercury switch 5| to closed pcsitlon.The rotation of the mercury switch 5| will Continue until the lower endof the lever 58 strikes shoulder 82 on plate 45 and prevents furthermovement of the lever 58. Any further rotation of the actuating rod 34by the bimetallic thermostat 33 will result in a separation of the stop40 on the strain release 31 from the finger 4|.

Moving the mercury switch 5| to closed position should reverse thetemperature trend so that the bimetallic thermostat 33 should now beginto heat up and rotate the actuating rod 34 in the opposite orcounter-clockwise direction as seen in Figure 2. The first thing thisrotation accomplishes is to return the finger 4| and the stop 40 intoengagement after which the strain release 31 will move pin 6| toward theleft as seen in Figure 2. This movement will cause the lever 58 torotate freely about the shaft 51 until the pin 60 engages the shoulder63 after which the lower end of the lever 58 will swing in a directionto rotate the mercury switch carrier 49 in a counter-clockwise directionabout the shaft 50 which will re- Any fur- 34 in a counter-clockin thestop 40 of the sult in opening the mercury switch 5|. ther rotation ofthe rod i ment is, concerned.

strain release "il separating' iront the finger 42.

It will be noted 'that 'the mercury switch 5i is mounted above its pivot50 and hence tends to remain in either o1 its actuated positions untilit is positively moved out of it.

It will be seen' that the spacing. hetw 'the shoulders 63 and 68 resultsin a free movement of the lever 58 4before it actuates the merciuyswitch 5 I. A certain denite temperature change is required in order forthe oimetallic thermostat 33 to rotate the pin 6i a distance sufficientto produce this free rotation of the lever 58. This arrangementtherefore provides for a deiinite differential of operation in themercury switch el and this differential of operation may he varied byadjusting the lever lit which varies the position of the shoulder @twith respect to the pin 60. In other words, if the lever 66? wererotated against the stop 33, the shoulder te would lie in engagementwith the pin E@ while that pin wes also in engagement with the shoulder63. 'Under these conditions the lever 58 would have no free Sellmovement :and would innnediately start to rom tate the mercury switch 5las soon as the pin 6i was moved by the 'actuating rod 3d. This 'would bethe condition wherein the differential of on eration was at its minimumvalue. 66 were rotated in the opposite direction until the finger 'l0engaged the shoulder llt on the plate i5 then the shoulder t8 of thelever 66 would coinm eide with the side t4 of the hole 59 in the plate45. Under these conditions the pin Si! would have a maximum movementbetween. the two shoulders and the differential of operation would be atits maximum value. illbviouslypv the differential of operation can headjusted to any value in he-l tween these two extreme values theadjustment of the lever 65.

It will be observed; that the plate 45 and the lever GS which, providethe shoulders between which the nin il@ operates mounted on the casingand that the manipulation of the lever 66 cannot put any strain whateverupon the thermal element 33 except that which may he imposed thereonthrough'the strain release 3l; Therefore this dierential adjustment ispracticallyioolproof as fer as damage to the instru The main adjustmentfor this instrument is accomplished hy rotating the arm 'l2 whichcarries with it the sleeve i1 and one end of the bimetallic thermostatt3. Olivi ously, a rotation of this arm adjusts the ternperature atwhich the thermostat 33 will actuate the mercury switch 5l. Y

It will he noted that the temperature at which the mercury switch ismoved to open position is determined only by the adjusting arm l2. Yliheadjustment of the lever S8 does not affect this operation because thenin til is against the fixed shoulder t3 when the mercury switch rotatedto onen position. The adjustment of the arm 66 in controlling thedifferential ci operation affects only the temperature at which theswitch 5i is reclosed, This feature is ci particular value in high limitcontrols wherein it is desired that the scale 8G should indicate thetemperature at which the switch opens regardless of the didier-n entialadjustment.

The modication disclosed in Figures and 6 is directed to a device whichis adapted to he mounted vertically instead of horizontal as in Figuresl to 4. in Figures 5 and ti the guard it, sleeve il, and himetallicthermostat S3 extend downwardly from the hase il. These elements aremounted however in the same manner as in lil If the lever ally mounted.

the irst modification and the adjusting disc i9 is connected to thesleeve il so that it may he rotated for adjusting the setting of thethermostat 33. The adjusting arm slightly dineren-t in thismodification. indicated at 89, is adjustably connected to the adjustingdisc ill in order to provide for a Calibrating adjustment and isprovided with an arcuate scale Sil and a y forwardly projecting arm 9ito facilitate manual rotation of the disc i9. The rod 3H is rotated bymeans of the thermostat 33 and this rod carries a scissors type strainrelease 3l as in the case of the rst modification.

A plate s2 is supported on posts St which are suitably secured to therear oi' the base H and the plate is fastened to these posts by means ofscrews 9d. Pivotally mounted to 'the plate 92 by means oi e, shaft lltis a mercury switch carrier 99 which carries a clip el in which ismounted the mercury switch 93 shown in dotted lines in Figure 6. Thelower end oi the mercury switch carrier il@ has a rearwardly andlaterally extending portion iilil for the purpose of supporting a shaftlili on which the floating lever m2 is pivot Tl lever ill2 has adownwardly extending tongue itli which extends between the two fingersil and 42 of the strain release connection carried by the rod 34. Theupper end of the lever lili? is provided with a pin it which extendsthrough a slot Hill in the plate t2. enditl' of the slot tilt limits themovement of the pin H35 toward the left as seen in Figure 5 and ashoulder itil on the diierential adjusting lever E09 limits the movementof the pin |05 toward the richt. The lever H19 is nivotally mounted onthe plate 32 coaxially with the mercury switch carrier Qt.' A springelement HD is mounted concentrically with the lever S09 and oers atric-tional resistance to the rotation of the lever it@ thereby tendingto maintain it in its adjusted position. lever ldd may he rotated in aclockwlzse direction until finger il? formed integrally therewithengages a shoulder H3 on the plate at which time the shoulder m8 will'he farthest removed from the shoulder lill and the differential will heat its maximum. If the lever ills is rotated until the ringer i12 islimited hy engagement with the shoulder H4 on the plate 42 the shoulderlili? will he moved until it is spaced from. the shoulder lill' only hythe width oi the pin. rlhis adjustment correspends to the minimumdifferential,

Assume that the lever the is adjusted as shown in Figure 5 and that thetemperature is at a relatively low value. The rod 34 has rotated thelever lili until the pin lil is against the shoulder 6,31 and will haverotated the mercury switch carrier to the position shown in Figures 5and S at which time the circuit through the mercury switch will heclosed. @n an increase in temperature the rod 31% will be rotated bymeans of the thermostat 3&3 to swine, the tongue M3 of the floatinglever im toward the left as seen in Figure 5. At this time the leverlili. will rotate freely about the sha't itl and move 'the pin H35against the shoulder lull. Further movement of the tongue itil towardthe left hy the rod 34 will swing the shaft lill toward the left aboutthe shaft 55 which will rotate the mercury switch carrier @il in aclockwise direction as seen in Figure 5 and cause the mercury switch tobe moved to coen circuit position. .any further rotation of the rod t@will he teiten un hy means of the strain release 3l and will have noeffect upon the lever ltll. @n a decrease in tempera One ture therotation of the rod 34 will be reversed and the strain release willfirst be taken up after which the tongue |03 of the lever |02 will beswung toward the right as seen in Figure 5 and the lever |02 will firstpivotvfreely about the shaft until the pin |05 engages shoulder |01after which further movement to the right of the tongue |03 will causethe shaft |0| to swing toward the right and rotate the mercury switchcarrier 96 to the position shown in Figure 5, at which time the circuitthrough the mercury switch 98 will be open. Any further rotation of therod 34 will of course be taken up by the strain release 31. The mercuryswitch 98 remains stationary during the differential action due to thefact that it has an over center mounting and hence must be positivelymoved from both of its limit positions.

It will be appreciated that adjustment of the lever |09 will vary theposition of the shoulder |08 and this adjustment varies the operatingdifferential of the switch from a maximum when the shoulder |08 isfarthest from shoulder |01, to a minimum where the shoulder |08 isseparated from shoulder |01 only by the width of the pin |05. In thelatter case there can be no lateral motion of the pin and any movementor" the tongue |03 will be immediately transferred to the mercury switch98 hence the differential of operation is at -a minimum under theseconditions.

Here as in the first modification the adjustment ofthe differential isaccomplished by means of the lever |09 which is pivoted to a memberfixed to the base of the casing, therefore no undue strain can be placedon the thermostatic element or the moving parts when the adjustmenttakes place. It is also clear that one of the limits of operation may beread directly on the scale 90 and the differential adjustment does notaffect this limit. In this particular case it is the temperature atwhich the switch is closed that is read on the scale 90 and which is notaffected by the differential adjustment, hence this particular devicewould be suitable as va low limit wherein that limit is the one which isadjustable by the arm 9| and which may be read directly on the scaleV90.

The modification disclosed in Figures 8 to 11, inclusive, is somewhatsimilar to the first modification described except that the parts havebeen so arranged that the scissors type strain release connection may beomitted. In this modification the thermostatic element mounting and thearm for adjusting the temperature setting of the thermostat are exactlythe same as in the first modification. Instead of the scissors typestrain lrelease, a crank arm |20 carrying a pin |2| is adjustablymounted on the shaft 34 by means of the set screw |22. A plate |23 isrigidly connected to the base by means of the posts |24 and screws (notshown). A mercury switch clip |26 is connected rigidly to a shaft |21pivoted in the plate |23. The clip |26 carries the mercury switch |28.On the other side of the plate |23 and rigidly connected to the shaft|21 is a second crank arm |29 which is U-shaped at the bottom as shownat |30 in Figure 8 to carry a shaft 3| on which the floating lever |32is pivotally mounted. The intermediate portion of the lever |32 isprovided with an elongated slot |33 which receives the pin |2|. Theupper end of the lever |32 carries a pin |35 which enters a generallyY-shaped slot |36 in the plate |23. The vertical leg of the Y is formedby a shoulder |31 of the slot |36 and the shoulder |38 carried by thedifferential adjusting lever |39 pivotally mounted on the shaft |21. Theflexible spring |40 offers a resistance to rotation of the lever |39whereby it tends to remain in its adjusted position. rlhe two legs |42and |43 of the Y- shaped slot are adapted to accommodate the pin |35 asthe lever |32 is rotated by the crank arm |20 in response to overruntemperatures, that is, temperatures which are well beyond the normalrange of the instrument.

The lever |39 is provided with the usual finger |45 which cooperateswith a scale |46 on the plate |23 to indicate the relative adjustment ofthe lever |39. This lever may be moved until the finger |45 abuts theshoulder |41 on plate |23 at which time the shoulder |38 will befarthest removed from the shoulder |31 and the differential of operationwill be at its maximum value. The lever |39 may be adjusted until thefinger |45 engages the shoulder |48 on the plate |23 at which time theshoulder |38 will be separated fromshoulder |31 by a distance equal tothe width of the pin |35. At this time the differential of operationwill be at its minimum value.

Inconsidering the operation of this device assume that the parts are inthe positions shown in Figures 7 and 8. At this time the temperature isat a relatively low value and the mercury switch is in closed position.Moreover, the temperature has decreased well below .the value at whichthe switch closed and the crank arm |20 has rotated in a clockwisedirection to a point where it has moved the lever |32 to a positionwhere the pin |35 is well up in leg |43 of the slot |36. As thetemperature begins to increase the crank arm |20 will begin to rotate ina counterclockwise direction as seen in Figure 7 or a clockwisedirection as seen in the remaining figures. This will result in rotatingthe lever |32 freely about the shaft |3| and moving the pin |35 towardthe left. The pin |35 will strike the opposite side of the slot |43 atwhich time the lever |29 will be rotated in a clockwise direction untilthe pin |35 clears the point |49 between the two legs |42 and |43 of theslot |36. The pin |35 will then move further to the left to engage theleft-hand side of the leg |42 as shown in Figure 9. Further rotation ofthe crank |20 will then result in a further rotation of the crank |29which will swing the shaft |3| in an arc to pull the pin |35 down intothe vertical leg |46 of the slot |36. The crank |29 will then be rotatedto a point Where the mercury switch |28 will be moved to open position.It will be noted that when the rotation of the mercury switch to openposition occurs the pin |35 is against the shoulder |31 of the verticalleg |43` of the slot |36. 1f the crank |20 should continue torotate inthe same direction the crank |29 will be rotated which will lift thelever |32 and the pin |35 in such a way that the pin |35 will pass upinto the leg |42 as seen in Figure 10.

On a decrease in temperature the rotation of the crank |20 will bereversed and the pin |35 will slide down the upper edge of the legv |42and the crank |29 will be rotated in a counterclockwise direction. Asthe pin |35 clears the point |48, it will pass 'to the opposite side ofthe slot |43 as seen in Figure 11. On further rotation of the crank |20the pin will be drawn downwardly into the leg |46 and against theshoulder |38. At this time the mercury switch will be rotated to closedposition and a further rotation `of the crank |20 will result in the pin|35 being movedup into the slot |43 as seen in Figure 8. Thus it is seenthat the position of the shoulder |38 determines the point at which themercury switch is rotated to closed position.

It will thus be seen that by providing. the legs |42 'and |43 in theplate |23 a substantial temperature Yoverrun is permitted in eachdirection without abnormal strain on the bimetallic ther- -mostat.

It will further be clear that the temperature at which the `mercuryswitch is moved to open position is determined by the shoulder |31 andthe temperaturev at ywhich the switch is moved to closedposition isdetermined by the shoulder |38. This latter temperature and hence thedifferential of operation of the device may be adjusted by rotating'`the lever ISS-to Vadjust the position of the shoulder |38. /Here againthe adjustment of the main adjustingarm will vary the temperature atwhiclrthe switch `is. opened and as the shoulder |31 is fixed thistemperature may be read directly onthe main scale. The adjustment of thelevery |39 therefore affects only the difference between thistemperature and the temperature at which the switch will be reclosed. Itwill also be noted that the differential adjustment yis accomplished byrotating the lever |39 which is mounted.v directly 'upon the plate |23fixed to the base v-||; Therefore no strain can be placed on thethermostatic element or driving connections by the careless`manipulation of the lever |39.-A 1

In these devices the casings havev been vmade ed Within them if desired.,The slots: |50 shown in Figure 7 have been providedfor this purpose. Itwillbeapprecated lt'hatthe"above described instrumentsmay be easilymodified for independent "on and "of control by making the'flxed stopadjustable also. In such a case temperature indicating. scales could'lbe i provided for cooperation with each stop'adjusting lever and themain adjustment would then be eliminated.

As many changes and modifications of this invention may occur tothose'who are skilled in the art it will be understood that I intend tobe limited by the scope of the appended claimsmovement in the oppositedirection, said last mentioned stop comprising an adjusting leverpivoted to said fixed support, and means for indicating the relativeadjustment of said second stop. f A

2. In a device of the character described, a support, a switch operatingmember pivoted to said support, a floating lever, a rst portion of saidfloating lever being pivotally connected to said member whereby thelatter may be rotated CII said stop means, after which said pivotalconnection moves to rotate said switch operating member, and straiilease ineens connecting said device and said .Y -iid portion.

3. In a device of the char., er described, a support, a switch operatingmember pivoted to said support, a floating lever, a first portion ofsaid floating lever being pivotally connected to said member whereby thelatter may be rotated by the formerja fixed lstop and a movable stop,said stopsglimiting the `movement in each direction of a secondportiiirof `said lever, a condition responsive device for moving a thirdportion of said lever back and forth whereby said lever first rotatesabout its pivotal:K connection with said member until said secondportion is limited in its movement by one of said stops, after whichsaid pivotal connection movesfto rotate said switch operating member,strain release means connecting said device and said third portion, andmeans for adjusting said movable stop whereby the differential ofoperation of said device may be varied.

4. In a device of the character described, a casing, a plate fixed tosaid casing, a pivotally mounted mercury switch, a rod rotated inaccordance with the changes in value of a variable condition,connections between said rod and said mercury switch, means fixed 0nsaid plate comprising a pair of stops for limiting the free movementofi-aV part of said connections for determining the differential ofoperation of said merof suchsize that a terminal board lmay be mounts'by the former, spaced stop means for limiting the movement in eachdirection of a second'portion of said lever, a condition responsivedevice for moving a third portion of said lever back and forth wherebysaid lever first rotates about its pivotal connection with said memberuntil said second portion is limited in its movement by cury switch, andmeansV including a single member movably mounted on said plate foradjusting one of said stops to determine said differential.

5. Ina device of the character described, a casing, a plate fixed tosaid casing, a pivotally mounted mercury switch, a rod rotated inaccordance with the changes in value of a variable condition,connections between said rod and Said mercury switch, means on saidplate comprising a pair of stops for limiting the free movement of apart of said connections for determining the differential vof operationof said mercury switch, one of said stops being fixed and the othercomprising a lever pivoted on said plate, means to adjust said lever andthereby vary said differential of operation, and means to indicate theposition of said lever.

6. In a device of the character-described, a casing comprising a baseand a cover therefor, a plate fixed to said base, a mercury switchcarrier pivoted on said plate, a bimetallic thermostat one end of whichis carried by said base, a. rod, the other end of said thermostat beingconnected to said rod to rotate it on variations in temperature, afioatng lever pivoted at one point to said mercury switch carrier, a`pair of stops on said plate, a projection on said floating lever forcooperation with one or the other of said stops, and means including astrain release mechanism connecting the floating lever for movement bysaid rod.

'7. In a device of the character described, a casing comprising a baseand a cover therefor, a plate fixed to said base, a mercury switchcarrier pivoted on said platea bimetallic thermostat one end of which iscarried by said base, a rod, the other end of said thermostat beingconnected to said rod to rotate it on variations in temperature, afloating lever pivoted at one point Yto said mercury switch carrier, apair of stops on said plate, a projection on said fioating lever forcooperation with one or the other of said stops, means connecting thefloating lever for movement by said rod whereby the diierential ofoperation of said mercury switch is determined by said stops, means foradjusting one of said stops whereby the temperature at which itch isoperated in one direction may be -dently varied, means for rotating saidone end of said thermostat with respect to said base, and meanscooperating with said rotatable means for indicating the temperature atwhich said mercury switch is actuated in the opposite direction.

8. In a device of the character described, a fixed plate, a pivotedmercury switch carrier, a floating lever one portion of which is pivotedto said carrier for actuatinglit, a hole in said plate, a projection onsaid lever extending tinough said hole, means on said plate for limitingthe movement of said projection in each direction, and conditionresponsive means engaging another portion of said floating lever formoving said projection into engagement with said limiting means andthereafter causing said lever to actua-te said mercury switch carrier,said hole being o such size and shape as to accommodate said projectionupon further movement of said lever by said condition responsive means.

9. En a device of the character described, a ined plate, a pivotedmercury switch carrier, a r'loatinCT lever one portion of which ispivoted to said carrier for actuating it, a hole in said plate, aprojection on said lever extending through said hole, means on saidplate for limiting the movement of said projection in each direction,and condition responsive means engaging another portion of said floatinglever for moving said projection into engagement with said limit-ingmeans and thereafter causing said lever to actuate said mercury switchcarrier, said lirniting means including a pivoted lever, and means toadjust said lever whereby the difierential of operation oi said mercuryswitch carrier may be varied, said hole in said plate being or' suchsize and shape as to accommodate further movement of said projectionupon overrun oi said condition responsive means.

l0. in a device of the character described, a

support, a switch actuating member pivoted to said support, a leverpivotally connected intermediate point to said switch actuatthe former,a condition responsive device for rroving one end or" said lever, meansincluding strain release mechanism connecting said de vice and said oneend, and stop means for limoi the character described, a operatingmember pivoted to ating lever, a first portion of lever' being pivotallyconnected to y said stop means, after which said piv and a two-waystrain release e n said condition responsive de ,ting lever wherebyoverrun of member whereby the latter is operated by i f' the movement ofthe other end of said said condition value does not place excessivestrain on said device.

12. A device of the character described comprising in combination, afixed support, a switch actuating member pivoted to said support, alever pivoted at one end to said member for rotating it about its pivot,a condition responsive device for moving the other end o! said lever,stop means for engaging an intermediate point on said lever to limit itsmovement and a strain release connection between said conditionresponsive device and said lever, whereby strain on said device due tooverrun of the value of said condition after actuation of said switch isrelieved.

13. In a device of the character described, a xed support, a switchactuating member pivoted to said support, a lever pivotally connected atan intermediate point to said switch actuating member whereby the latteris operated by the former, a condition responsive device for moving oneend of said lever, stop means engageable with the other end of saidlever to limit its movement, and a strain release connection betweensaid condition responsive device and said lever, whereby strain on saiddevice due to overrun of the value of said condition after actuation ofsaid switch is relieved.

14. In a device of the character described, a casing comprising a baseand a cover therefor, a plate xed to said base, a mercury switch carrierpivoted on said plate, a bimetallic thermostat one end of which iscarried by said base, a rod, the other end of said thermostat beingconnected to said rod to rotate it on variations in temperature, saidthermostat and rod projecting horizontally through the back of saidcasing, a floating lever pivoted at one point to said mercury switchcarrier for movement in a vertical plane, a pair of stops on said plate,a projection on said floating lever for cooperation with one or theother of said stops, a pin extending horizontally from said lever, and astrain release mechanism on said rod comprising a pair of oppositelybiased fingers extending vertically on opposite sides of said pin, saidpin and strain release mechanism forming a driving connec tion betweensaid rod and said lever, whereby strain on the thermostat due to overrunafter actuation oi said switch is prevented.

15.111 a device of the character described, a casing comprising a baseand a cover therefor, a plate xed to said base, a mercury switch carrierpivoted on said plate, a bimetallic thermostat one end of which iscarried by said base, a rod, the other endl of said thermostat beingconnected to said rod to rotate it on variations in temperature, saidthermostat and rod projecting vertically through said casing, a floatinglever pivoted at one point to said mercury switch carrier for movementin a vertical plane, a pair of stops on said plate, a projection on saidfloat* ing lever for cooperation with one or the other of said stops,and a strain release mechanism on said rod comprising a pair ofoppositely biased iingers extending horizontally on opposite sides ofsaid lever, said strain release mechanism forming a driving connectionbetween said rod and said lever, whereby strain on the thermostat due tooverrun after actuation of said switch is prevented.

STEPHEN CRUM.

